#include <future>
#include <iostream>

bool is_prime(int x)
{
    for (int i = 2; i < x; i++)
    {
        if (x % i == 0)
            return false;
    }
    return true;
}

int main()
{
    // std::future<bool> fut = std::async(is_prime, 700020007);
    // std::cout << "please wait";
    // std::chrono::milliseconds span(100);
    // while (fut.wait_for(span) != std::future_status::ready)
    //     std::cout << ".";
    // std::cout << std::endl;

    // bool ret = fut.get();
    // std::cout << "final result: " << ret << std::endl;

    uint32_t head_size = 25;
    std::string send_str;
    send_str.insert(0, std::string((const char *)&head_size, 4));
    std::cout << send_str << "-" << send_str.size() << std::endl;

    return 0;
}